Various 4-(5-halomethyl-2-pyridyloxy)phenoxy compounds are known to be useful as herbicides as disclosed in European Published Patent Application No. 483, United Kingdom Patent Specifications Nos. 1,599,121 and 1,599,126 and U.S. Pat. Nos. 4,184,041 and 4,317,913. For example, butyl 2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy]propionate which is also known as fluazifopbutyl is an effective grass herbicide which can be used in fields where broad-leaved crops such as cotton and soybeans are cultivated. Important starting materials for such pyridyloxyphenoxy compounds are the 2-halo-5-trichloromethylpyridines such as 2-chloro-5-trichloromethylpyridine described in U.S. Pat. No. 4,317,913. Such 2-halo-5-trichloromethylpyridines, in turn, may be prepared by chlorinating, under ultraviolet light irradiation, a 2-halo-5-methylpyridine as described in U.S. Pat. No. 4,152,328.
An object of the present invention is an efficient, economical and reliable synthesis of 2-halo-5-methylpyridines as well as intermediates used in the synthesis.
A further object of the present invention is a method for preparing 2-halo-5-methylpyridines without utilizing pyridine, and in particular 3-picoline, starting materials to thus avoid the problems of byproduct formation in the halogenation reaction to yield (I) wherein X is halogen.